Abstract

Physical and chemical disinfection methods are used or are under investigation in greenhouse facilities to minimize the occurrence of pathogens and the application of pesticides in recirculating systems. Since the most of these methods differ in their effectiveness, more investigation is needed to produce healthy plants in a sustainable way. Therefore, the present study is focused on the identification of interactions between hypochlorite (ClO−) used as a disinfectant for a recirculating system and algae formation, spread of microorganisms, as well as plant development. As such, on-site produced potassium hypochlorite (1 % KClO) solution were supplemented using proportional injection control once a week for 90 min, as a disinfectant, into a recirculating tomato production system (NFT) until a free chlorine concentration of 1 mg L−1 (D I) and 2 mg L−1 (D II) were reached, respectively.

The formation of the algae biofilm was reduced by 15 % (D I) and 48 % (D II). These treatments also suppressed cultivated microorganisms up to 100 %. Tomato plants exposed to the treatment D I showed a comparable plant height to the control plants after 7 weeks, whereas D II led to a significant increase in plant height of 12 cm. However, the formation of leaves was more pronounced by treatment D I. After a growing period of 7 weeks, a significant difference in leaf number up to 2.9 leaves per plant was calculated compared to the other treatments. The same treatment had the largest positively impact on the fruit yield and number of fruit, which were increased by 10 and 15 %, respectively, compared to the control plants.

Under consideration of all results, the most promising effects of ClO− as a disinfectant for hydroponic systems were achieved with a free chlorine concentration of 1 mg L−1 (D I), where phytotoxic effects can be excluded.